This would come a few days away from the point when Gov. Chris Gregoire, Mayor Greg Nickels and King County Executive Ron Sims are to make the final decision among themselves about how to replace the central part of the viaduct, between Pioneer Square and the Battery Street Tunnel.

Drago said she thinks council members will endorse a variation of one "surface" replacement option that would disperse traffic over six lanes on Alaskan Way and Western Avenue, through a series of traffic signals and into the Battery Street Tunnel.

That option, estimated to cost $900 million exclusive of yearly maintenance and operation expenses, would involve additional transit service and the addition of a northbound lane on Interstate 5 to handle the traffic.

Engineers studying the eight replacement options said they plan by next week to narrow the field to three options from which the finalist can be picked. Some council members said they may weigh in at the same time, perhaps in favor of a "surface" option; several members have said in the past they supported that idea.

That option is "basically the council's plan," Drago said Monday after more than two hours of briefings from viaduct staffers. Conlin said the eventual pick may combine elements of the surface option and others and council members will discuss it after the choices are narrowed to the three semi-finalists.

Councilman Tim Burgess said traffic-analysis data from the three agencies tells him any of the eight options could handle traffic without causing major congestion on I-5. Analysis of the surface options shows "that it's very viable and protects freight mobility," he said.

Drago said she favors replacing the viaduct with a tunnel, but high cost argues against doing that immediately. A surface dispersal of traffic from the 1950s-vintage viaduct is "what you would need to do" to improve flow on downtown streets and get more people onto buses, she said, adding that a tunnel could be built separately later.

Two tunnel replacements range in cost from $2.7 billion for a "cut and cover" construction type to $3.5 billion for one bored with drilling machines between the sports stadiums and Aurora Avenue. A highway in a partially lidded trench would cost an estimated $1.9 billion. Council members said there's been no recent talk of assessing waterfront landowners to help pay for a tunnel.

Council action, if it comes, would follow completion of economic-impact studies of viaduct replacements, designed to show how replacements would affect downtown businesses and the regional economy. Results of those are expected to be presented Thursday at a stakeholders' committee session scheduled for 4 to 7:30 p.m. at City Hall.

Other standards for replacing the viaduct include maintaining efficient movement of people and goods, improving the environment and safety, improving the waterfront as a place for people, and solutions that "are fiscally responsible," according to published guidelines.

Construction costs include removing waterfront streetcar tracks and replacing the Elliott Bay sea wall between Washington and Pike streets but not the cost of other traffic-management measures such as adding more streetcars or bus-only lanes to streets, a lane on I-5 or widening Mercer to handle east-west traffic.

Those costs range from $4 million to $641 million on measures ranging from transit incentives to new streetcar lines.